Field of the Disclosure
The present disclosure relates to an image processing apparatus, an image processing method, and a program for processing moving images.
Description of the Related Art
A recursive noise reduction processing technique is known as a conventional technique for executing a noise reduction process on moving image signals. According to the recursive noise reduction processing technique, two frames consecutive in a temporal direction of moving image (i.e. an input signal of the current frame and an output signal of the previous frame) are blended to reduce random noise generated in the temporal direction. As a method for setting the blend ratio between signals of two frames consecutive in the temporal direction (hereinafter, the ratio is referred to as recursive coefficient), there is a known method, for example, as described in Japanese Patent Laid-Open No. 2000-224444. According to the method described in Japanese Patent Laid-Open No. 2000-224444, the amount of change between two frames is calculated and the recursive coefficient is set depending on the amount of change. In this manner, setting the recursive coefficient depending on the amount of change between frames allows a noise reduction process adapted to whether the subject seen in moving image is a stationary subject or a moving subject.
In many cases, the moving image subjected to a recursive noise reduction processing is a moving image with an insufficient signal-to-noise ratio (SN) ratio, such as a moving image captured under dark environments such as at a dark place or during the hours of darkness. When the moving image has an insufficient SN ratio, accuracy of the calculated amount of change between the frames becomes low under influence of noise in the images. In addition, in the recursive noise reduction processing described in Japanese Patent Laid-Open No. 2000-224444, when the accuracy of the calculated amount of change between frames is low, no appropriate value of recursive coefficient can be obtained. In this case, afterimages (image trailing) may occur around a moving subject or noise (in particular, color noise) may remain in a stationary subject.